JPS6329695B2 - - Google Patents

Abstract

A fluorinated polymer having pendant cation exchange groups selected from sulfonic acid, carboxylic acid or sulfonamide groups, or their salts, is modified with a sulfonium compound and/or a phosphonium compound for substitution of the counter-ions of the cation exchange groups with sulfonium ions and/or phosphonium ions. The polymers treated in this manner are improved in their melt-flow characteristic to make fusion bonding between these polymers possible. The process is particularly suitable for repairing damaged cation exchange membranes for use in chlor-alkali electrolytic cells to advantageously elongate the life of the membranes.

Description

Detailed Description of the Invention The present invention provides fluorine-based cations having one or more functional groups selected from sulfonic acids and their salts, carboxylic acids and their salts, sulfonamides and their salts in their side chains. This invention relates to a fusion bonding method for exchange membranes. It is well known that fluorine-based cation exchange membranes having functional groups such as sulfonic acid groups, carboxylic acid groups, and sulfonamide groups are particularly useful as ion exchange membranes for separating the anode and cathode of chloralkali electrolytic cells. There is. These ion exchange membranes may suffer damage such as tears, pinholes, and cracks during use. The electrolytic performance of the damaged membrane deteriorated, and it could not be continued or reused.
If such a damaged membrane could be repaired and reused, it would be very effective to extend the life of the expensive fluorine-based ion exchange membrane.

One possible method for repairing such damaged membranes is to overlay the same membrane on the damaged area and melt-bond it, but fluorine-based ion-exchange membranes decompose before they melt when the temperature is increased by heating. This makes fusion bonding difficult. In contrast, the present inventors
No. 54-155273 discloses a method of heat-melting bonding in the presence of an aqueous medium.

This method is quite useful as a fusion bonding method for small damaged areas, but because it requires relatively high temperature and pressure conditions, it cannot be said to be a fully satisfactory fusion bonding method for large damaged areas. do not have.
Therefore, in order to solve these drawbacks, the present inventors investigated a method for melt joining fluorine-based polymers having cation exchange groups, and found that the fluorine-based polymers were treated with a sulfonium compound or a phosphonium compound. The present invention was completed by discovering that at least the surface of the polymer melts and flows at relatively low temperatures and low pressures.

That is, the present invention relates to a method for melt-bonding fluoropolymers having one or more functional groups selected from sulfonic acids and salts thereof, carboxylic acids and salts thereof, and sulfonamides and salts thereof in their side chains. At least one of the polymers is treated with a sulfonium compound and/or a sulfonium compound.
Or a method of improving the fluidity of the polymer by exchanging the counter ion of the cation exchange group with a sulfonium ion and/or phosphonium ion by treatment with a phosphonium compound, thereby enabling melt bonding without decomposition. It provides:

Next, the present invention will be explained in detail.

The fluoropolymer of the present invention has the general formula - (OCF ₂ - CFY) _l - (O) _n - (CFY') _o -X where Y and Y' are each F or C ₁ to C ₁₀ perfur Oralkyl group, l=0-3, m=0-1,
n = 0 to 12, The invention is not limited. A typical method for producing the fluoropolymer used in the present invention is to copolymerize and mold at least one monomer selected from each of the two groups shown below. The first group of monomers are fluorinated olefin compounds, such as tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, and vinylidene fluoride.

The second group of monomers has the general formula - (OCF ₂ CFY) _l - (O) _n - (CFY') _o (X') where Y and Y' are each F or a part of C ₁ to C ₁₀ . Fluoroalkyl group, l=0-3, m=0-1,
It is an olefin compound having a sulfonyl fluoride group or a carboxylic acid ester group, where n=0 to 12 and (X')=sulfonyl fluoride or an alkyl ester consisting of _C1 to _C10 of carboxylic acid. For example, CF ₂ = CFO (CF ₂ ) ₂ - SO ₂ F, CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ - SO ₂ F, CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₃ SO ₂ F, CF ₂ = CFO [CF ₂ CF (CF ₃ ) O] ₂ (CF ₂ ) ₂ SO ₂ F, CF ₂ = CF (CF ₂ ) ₂ SO ₂ F, CF ₂ = CFO (CF ₂ ) ₃ COOCH ₃ , CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ COOCH ₃ , CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₂ COOCH ₃ , CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₃ COOCH ₃ , CF ₂ =CFO [CF ₂ CF (CF ₃ )O] ₂ (CF ₂ ) ₂ COOCH ₃ , etc.

The amount of functional groups is expressed in equivalent weight (number of grams of polymer containing 1 g equivalent of functional groups) and is usually 400 to 2000.
It is copolymerized to become

Also, JP-A-52-24176, JP-A-53-132094
Fluorinated polymers in which part or all of the sulfonyl groups are converted into carboxylic acid groups or derivatives thereof by chemical treatment may also be used, as described in JP-A-54-83982.

The melt bonding method of the present invention is not limited to the shape of the polymer, and is effective for melt bonding all types of polymers, such as membranes, particles, and powders, and is also effective for melt bonding of all types of polymers, such as film-like, granular, and powder-like materials. It is valid.

In order to convert the functional groups of the obtained polymer into sulfonic acid groups and carboxylic acid groups, if necessary, the polymer is treated under general saponification conditions such as treatment with an aqueous alcoholic alkali solution. In addition, in order to convert the sulfonamide group to a sulfonyl fluoride group, ammonia,
Treat with alkylamine, etc.

The salt of the fluorine-based polymer used in the present invention is preferably an alkali metal salt (eg, Na, K) or an ammonium salt.

Next, the counter ion of the cation exchange group of the fluorinated polymer used in the present invention will be explained.

In melt bonding of fluorine-based polymers, the counter ion of the cation exchange group is very important in improving the fluidity of the polymer. Surprisingly, by using a sulfonium ion or a phosphonium ion as the counter ion, the fluidity of the polymer is greatly improved and melt bonding can be easily performed.

Here, the sulfonium ion has the general formula [R ₃ S] ⁺
refers to the compound represented by R is, for example, an alkyl group, an aryl group, or an aralkyl group, and is preferably an alkyl group or an aralkyl group.
[R ₃ S] One of the R's in the compound represented by ⁺ may be a hydrogen group. Alkyl group has 1 to 10 carbon atoms
Those with numbers 1 to 7 are preferred, and those with numbers 1 to 7 are particularly preferred. The aryl group preferably has 6 to 10 carbon atoms, particularly 6 or 7 carbon atoms. The aralkyl group preferably has 7 to 10 carbon atoms, and particularly preferably has 7 carbon atoms. Specific examples of the sulfonium ion used in the present invention include trimethylsulfonium ion, triethylsulfonium ion, tribenzylsulfonium ion, and the like.

The phosphonium ion used in the present invention is a compound represented by the general formula [R' ₄ P] ⁺ . R' is, for example, an alkyl group, an aryl group, or an aralkyl group, and is preferably an alkyl group or an aryl group. One or two R's of the compound represented by [R' ₄ P] ⁺ may be a hydrogen group. The alkyl group preferably has 1 to 10 carbon atoms, particularly 1 to 7 carbon atoms.
Preferably. Aryl group has 6 carbon atoms
-10 is preferable, and 6 and 7 are especially preferable. The aralkyl group preferably has 7 to 10 carbon atoms, and particularly preferably has 7 carbon atoms.

Particularly preferred is a quaternary phosphonium ion in which all four R's are substituted with alkyl or aryl groups.

Examples include tetramethylphosphonium ion, tetraethylphosphonium ion, tetraphenylphosphonium ion, and the like.

Next, to replace the counter ion of the cation exchange group of the fluorine-based polymer with a sulfonium ion or phosphonium ion, a sulfonium base or its salt ([R ₃ S] ⁺ X ^- , X ^- = OH ^- or halogen ion) is used. ,
Phosphonium base or its salt ([R′ ₄ P] ⁺ X ^- , X ^-
This can be easily carried out by an ion exchange method by bringing the fluorine-based polymer into contact with an aqueous solution of (=OH ^- or halogen ion).

Water is preferred as the solvent. However, in order to improve solubility, a mixed solvent with an organic solvent such as alcohol or ketone may be used if necessary.

When replacing the counter ion of a cation exchange group by the ion exchange method, the counter ion (e.g. Na ⁺ , K ⁺
It is preferable to keep the concentration of (ions, etc.) as low as possible.

The concentration of sulfonium and/or phosphonium ions is generally 0.01 to 0.5 normal.

Regarding the degree of substitution, the effect differs depending on the amount of substitution, but if 10% or more of the counter ions of all the cation exchange groups are substituted, the flow characteristics are sufficiently improved and melt bonding becomes easy. However, although effects can be seen depending on the degree of substitution even if it is less than 10%, it is preferable to substitute 10% or more.

In the present invention, when fluorine-based polymers having cation exchange groups are the same, or when two or more types of polymers are melt-joined,
Each cation exchange group, its equivalent weight, molecular weight, etc. may be different from each other. In this case, the effect of the present invention can be sufficiently achieved when the counter ion of the cation exchange group of only one piece is a sulfonium ion and/or a phosphonium ion in the case of melt joining. Of course, the counterions of both polymers may be replaced.

Melt bonding replaces the counter ions of at least one exchange group of the polymers to be bonded with sulfonium ions and/or
Alternatively, after forming phosphonium ions, the phosphonium ions are heated and pressed in a dry or wet state.

This is a method in which a small piece of the polymer (hereinafter referred to as a patch) is applied to a damaged area and melt-bonded, and only the patch needs to be treated with a sulfonium compound or phosphonium compound, and is very effective in practice.

As a heating method, heating with a hot plate, ultrasonic heating, impulse heating, friction heating, high frequency heating, etc. are used, but ultrasonic heating is superior in terms of workability. The heating humidity and pressing pressure vary depending on the molecular weight of the polymer, the presence or absence of reinforcing material, the type and shape of the exchange group, the substitution ratio of sulfonium ions and/or phorphonium ions, etc., but it cannot be stated unconditionally, but from 150 ° C.
300°C is common, and it is usually carried out at 200-260°C. Pressure is effective for melt joining, but generally 3 to 20 Kg/ ^cm2 , preferably 5 to 10
Performed in Kg/cm ² . When using ultrasonic waves, the horn tip amplitude is generally 50 to 300 microns and the pressure is 5
~60Kg/cm ² , and the application time is selected from the range of 0.1 to 10 seconds.

The polymers melt-bonded as described above are bonded firmly enough to withstand boiling in water, a 5N aqueous solution of caustic soda, and a mixed solvent of water and methanol.

The present invention has been described in detail above, and according to the method of the present invention, one or more functional groups selected from sulfonic acids and their salts, carboxylic acids and their salts, sulfonamides and their salts are added to the side chain. By treating at least one side of the fluorine-containing polymer that is likely to decompose before melting with a sulfonium compound and/or a phosphonium compound, the counter ion of the cation exchange group can be changed to a sulfonium ion and/or By substituting phosphonium ions, the fluidity of the polymer is improved and melt bonding becomes possible. The present invention is particularly effective as a method for repairing damaged parts of cation exchange membranes for chlor-alkali electrolysis by melt-bonding.

Furthermore, by using the method of the present invention, fluorine-based cation exchange membranes can be easily joined and processed into a cylindrical or bag shape. Since the product processed in this way can be suitably attached to, for example, a finger-type electrolytic cell, the electrolytic cell using the conventional asbestos diaphragm method can be used as is and converted to the ion exchange membrane method, which is a great economic advantage.

This will be explained in detail in Examples below.

Example 1 CF ₂ = CF ₂ with a copolymerization ratio of 1500 in terms of equivalent weight
CF ₂ = CFOCF ₂ CF (CF ₃ ) A 0.4 mm thick film made of a copolymer with OCF ₂ CF ₂ SO ₂ F and reinforced with polytetrafluoroethylene fibers was mixed with 15% potassium hydroxide and 30%. -SO ₂ F in the polymer side chain was converted to -SO ₃ K by treatment with a solution consisting of methanol and 55% water.

Two sheets of this film-like polymer were placed in a 0.1N aqueous solution of trimethylsulfonium iodide for 10 minutes at room temperature.
Soaked for a period of time. Layer the two sheets in a wet state and heat press at a temperature of 240℃ and a pressure of 10Kg/ ^cm2 for 5 minutes.
I went for a minute. This product had adhesive strength that withstood boiling in a 5N aqueous solution of caustic soda for 10 hours.

Example 2 CF ₂ = CF ₂ with a copolymerization ratio of 1100 in terms of equivalent weight
CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₃ A 0.3 mm thick film made of a copolymer with SO ₂ F was saponified under the same conditions as in Example 1 to form a polymer side chain. -SO ₂ F was converted to -SO ₃ K. This material was treated with 2N hydrochloric acid to form -SO ₃ H. Only one of the two sheets was made into a sulfonium type by immersing it in a 0.25N tetraethylphosphonium base aqueous solution for 1 hour at room temperature. this-
Layer it on SO ₃ H type film and keep it moist.
Hot pressing was performed for 6 minutes at a temperature of 260° C. and a pressure of 8 Kg/cm ² . This item was strongly bonded to the extent that it could withstand boiling water.

Example 3 CF ₂ = CF ₂ with a copolymerization ratio of 1200 in terms of equivalent weight
CF ₂ = CFOCF ₂ CF (CF ₃ ) By treating a 0.4 mm thick film-shaped copolymer with OCF ₂ CF ₂ SO ₂ F with ethynediamine, a part of the SO ₂ F is converted into sulfonamide. Converted to base. 15% of this
It was hydrolyzed and converted to the sodium form by treatment with a solution consisting of sodium hydroxide, 30% methanol, and 55% water. This material was treated with a 0.15N aqueous tetramethylphosphonium base solution at room temperature for 15 hours. These two sheets were stacked and melted and bonded using an ultrasonic welder at a horn tip amplitude of 200 microns and a pressure of 35 kg/cm ² for 2 seconds. The bond was strong enough to withstand boiling of a mixed solution consisting of 15% sodium hydroxide, 30% methanol, and 55% water.

Example 4 CF ₂ = CF ₂ with a copolymerization ratio of 1300 in terms of equivalent weight
CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₃ A 0.4 mm thick film made of a copolymer with SO ₂ F and reinforced with polytetrafluoroethylene fibers was prepared in the same manner as in Example 1. The --SO ₂ F group was converted to --SO ₃ K group by saponification using . Two sheets of this film-like polymer were treated with a 0.15N aqueous solution of trimethylsulfonium iodide at room temperature for 5 hours. Layer two sheets of this and use an ultrasonic welder to make the horn tip amplitude 120.
Welding was carried out for 3 seconds at a pressure of 28 kg/cm ² . This item was strongly bonded to the extent that it could withstand boiling water.

Example 5 CF ₂ = CF ₂ with a copolymerization ratio of 1100 in terms of equivalent weight
CF ₂ = CFO (CF ₂ ) ₃ Thickness due to copolymer with COOCH ₃
A 0.3 mm film-like molded product was treated under the same saponification conditions as in Example 1, and _three COOCH units were added to the COOK.
Converted to . This material was treated with a 0.15N aqueous tetramethylphosphonium base solution at room temperature for 15 hours. Two of these were stacked and welded together using an ultrasonic welder at a horn tip amplitude of 150 microns and a pressure of 30 kg/cm ² for 1 second. This product was firmly bonded to the extent that it could withstand boiling in a 5N aqueous sodium hydroxide solution.

Example 6 CF ₂ = CF ₂ and CF ₂ = CFOCF ₂ CF (CF ₃ )
OCF ₂ CF ₂ SO ₂ F and 1,1,2-trichloro-
Copolymerization was carried out in 1,2,2-trifluoroethane using perfluoropropionyl peroxide as a polymerization initiator while maintaining the polymerization temperature at 45° C. and the pressure at 5 kg/cm ² . This will be referred to as Polymer-1. Copolymerization was carried out in the same manner while maintaining the pressure at 3 Kg/cm ² .
This will be referred to as Polymer-2.

A portion of each of these polymers was hydrolyzed in a mixed solution of 5 N caustic soda aqueous solution and methanol (volume ratio 1:1) at a temperature of 90°C for 16 hours to form a sodium sulfonate form. As measured, Polymer-1 was 0.74 milliequivalent/g - dry resin, Polymer-2 was 0.91 milliequivalent/g
g - It was a dry resin. Polymers-1 and -2 were heat-molded to form films of 50 microns and 100 microns, respectively, and then both films were combined and heat-formed to form a laminate film.

This membrane was saponified in 2.5N caustic soda/50% methanol at 60° C. for 16 hours, returned to the H form in 1N hydrochloric acid, and then converted to the NH ₄ form by treating with a 1N NH ₄ OH aqueous solution for 5 hours. PCl ₅ /
It was treated in a POCl ₃ solution at 100°C for 30 hours to convert it into a sulfonyl chloride group. CCl ₄ after reaction completion
When the surface infrared spectrum was measured, it was found to be 1420 cm ^-1 which is the characteristic absorption of sulfonyl chloride.
Absorption was strongly observed, and even when stained with crystal violet, the membrane was not stained at all. The two membranes were clamped between acrylic resin frames using a polytetrafluoroethylene gasket with the polymer-1 side facing outward. Polymer-1 immersed in 57% hydroiodic acid aqueous solution at 80℃ for 24 hours
Only one side of the side reacted.

Afterwards, when the cross section was stained with crystal violet, 20 microns of the surface was stained blue, and carboxylic acid was confirmed by surface infrared spectrum. This membrane was placed in chlorine gas at room temperature and normal pressure for 5 minutes.
After treatment for an hour, the mixture was treated in 2.5N caustic soda/50% methanol at 90°C for 40 hours to convert it into the sodium salt form of sulfonic acid and carboxylic acid. In this way, a fluorine-based cation exchange membrane having carboxylic acid groups on one surface and sulfonic acid groups on the other surface was produced. Two of these cation exchange membranes were placed in a 0.15 N trimethylsulfonium iodide aqueous solution at room temperature for 15 min.
It was immersed for a period of time to form a sulfonium ion type. This 2
Layer the polymer sheets so that the two sides are in contact at a temperature of 250°C.
Heat pressing was performed for 5 minutes at a pressure of 10 kg/cm ² . This product had adhesive strength that withstood boiling in a 5N aqueous solution of caustic soda for 10 hours.

Example 7 10g in a 300c.c. stainless steel autoclave
CF ₂ = CFOCF ₂ CF (CF ₃ ) O (CF ₂ ) ₃ SO ₂ F,
After emulsifying 95 c.c. of water containing 1 ppm copper sulfate, 0.18 g of ammonium persulfate, 2.0 g of sodium hydrogen phosphate, and 1.9 g of ammonium perfluorooctanoate, add 5 c.c. of 0.16% sodium bisulfite solution. c. While maintaining the temperature at 40° C., tetrafluoroethylene was copolymerized at a pressure of 4 kg/cm ² , and the pressure of tetrafluoroethylene was controlled so that the polymerization rate was constant.

The obtained polymer contained 2.47% by weight of sulfur according to elemental analysis, and when a part of the polymer was hydrolyzed and the ion exchange capacity was measured.
0.72 meq/g - dry resin.

The above sulfonyl fluoride type polymer was molded into a film with a thickness of 250 microns, and the following Example 6
A fluorine-based cation exchange membrane having carboxylic acid groups on one surface layer was obtained in the same manner as above. Two sheets of this cation exchange membrane were immersed in a 0.10 N tetramethylphosphonium base aqueous solution to convert it into a phosphonium ion type. These two sheets were stacked so that the sulfonic acid sides were in contact with each other and heated and pressed at a temperature of 270° C. and a pressure of 7 kg/cm ² for 4 minutes. This product had sufficient adhesive strength to withstand treatment with a 2.5N caustic soda water/methanol solution (volume ratio = 1:1) at a temperature of 60°C for one day.

Example 8 Two membranes having a carboxylic acid group and reinforced with a tetrafluoroethylene fibrous material prepared in the same manner as in Example 5 and having a width of 100 cm and a length of 130 cm were used. The periphery of these membranes over a width of about 10 cm was treated with an aqueous solution of trimethylsulfonyl iodide for 15 hours at room temperature.

Next, these two membranes were stacked and the edges of one width direction and two length sides were heated at a temperature of 260℃ and a pressure of 10℃.
Heat pressing was performed at Kg/cm ² for 5 minutes to join and form a bag.

The bond was strong enough to withstand boiling of a mixed solution consisting of 15% sodium hydroxide, 30% methanol, and 55% water.

Example 9 A membrane with a short side of 130 cm and a long side of 250 cm, reinforced with a fibrous material and having a carboxylic acid group on one side and a sulfonic acid group on the other side, was created in the same manner as in Example 6. .

Both short sides of this membrane, approximately 10 cm wide, were soaked in a 0.2 N tetraethylphosphonium base aqueous solution at room temperature.
Soaked for 10 hours.

Next, the two short sides were overlapped so that the carboxylic acid group surface and the sulfonic acid group surface were the bonding surfaces, and welded using an ultrasonic welder with a horn tip amplitude of 150 microns and a pressure of 30 kg/
A cylindrical membrane was formed by melt-bonding at cm ² for 30 seconds.

This product had adhesive strength that withstood treatment in a 6.5N caustic soda aqueous solution at 90°C for more than 30 days.

Example 10 Having a carboxylic acid group in the same manner as in Example 5,
A membrane reinforced with tetrafluoroethylene fibrous material was created.

This film was melt-bonded using an ultrasonic welder in the same manner as in Example 9 to form a cylindrical film.

This product had adhesive strength that withstood treatment in a 6.5N caustic soda aqueous solution at 90°C for more than 30 days.

Claims (1)

[Scope of Claims] 1. A fluorinated polymer having one or more cation exchange groups selected from sulfonic acids and their salts, carboxylic acids and their salts, sulfonamides and their salts in their side chains. In the method of mutually melting and joining,
A method for melt joining, which comprises replacing the counter ion of at least one of the ion exchange groups of the polymer with a sulfonium ion and/or a phosphonium ion, and then performing melt joining. 2 The fluorine-based polymer has the general formula -(OCF ₂ CFY) _l -(O) _n -(CFY') _o -X where Y and Y' are each F or a C ₁ to C ₁₀ perfluoroalkyl group. , l=0-3, m=0-1,
Claim 1 where n=0 to 12, X=side chain structure represented by a sulfonic acid group, a carboxylic acid group, a sulfonamide group, or a salt thereof
The method described in section. 3. The method according to claim 1, wherein at least 10% of the counterions of the cation exchange group are sulfonium ions and/or phosphonium ions. 4. The method according to claim 1, wherein the counter ion of only one cation exchange group of the fluorine-based polymer is a sulfonium ion and/or a phosphonium ion. 5. Claim 1 in which the sulfonium ion is represented by the general formula [R ₃ S] ⁺ , and R is an alkyl group having 1 to 10 carbon atoms or an aralkyl group having 7 to 10 carbon atoms.
The method described in section. 6. The method according to claim 1, wherein the phosphonium ion is represented by the general formula [R' ₄ P] ⁺ , and R' is an alkyl group having 1 to 10 carbon atoms or an aryl group having 6 to 10 carbon atoms. . 7. The method according to claim 1, wherein the fluorine-based polymer is a fluorine-based cation exchange membrane reinforced with fluorine-based fibers. 8. The method according to claim 1, wherein the fusion bonding is performed using ultrasonic waves. 9. The method according to any one of claims 1 to 8, wherein the fluorine-based polymer is melt-bonded to form a cylindrical membrane or a bag-shaped membrane.